The present invention relates to an internally axed single-rotation machine. This denomination means that an external and internal rotor are provided and each rotates around a single axis which does not change its position relative to a common casing surrounding both rotors. The rotors form as a result of their reciprocal engagement working spaces with a variable volume and openings on the circumference of the external rotor control the charge change.
A machine of this type is e.g. known from German Pat. No. 1024196. The arrangement of the rotors is comparable with that of a hollow gear and a pinion positioned therein. In the case of such machines, the engagement parts of the external rotor are relatively thin-walled beside the control openings thereof and can therefore be bent out by the pressure of the working medium and in particular by centrifugal forces. In addition, all the engagement parts of the external rotor, particularly in the case of an axially extended design of the machine are exposed to bending forces. In order to avoid such thin-walled regions, it is possible to increase the external rotor diameter. However, this leads to an enlargement of the dead spaces present at the control openings.